This invention relates to a process for the carbonylation of a saturated hydrocarbon to give an oxygenated saturated hydrocarbon. The process involves using a solid strong acid catalyst, such as sulfated zirconia, to catalyze the carbon monoxide addition to the saturated hydrocarbon at reaction conditions to form oxygenates. The oxygenate can be subsequently hydrogenated to provide reduced oxygenates, e.g., ketones can be hydrogenated to alcohols. Alternatively, a hydrogenation component can be added to the solid strong acid catalyst such that reductive carbonylation takes place in one step.
Industrial chemicals, to a large extent, contain heteroatoms (O, N, S and halide) prepared by processes in which hydrocarbons are converted to organic compounds containing various heteroatoms. Although saturated hydrocarbons such as paraffins and naphthenes are the lowest cost and most readily available hydrocarbons; they are also very stable and thus not very chemically reactive. Therefore, the most common route to preparing various hetero organic compounds has been to first convert the saturated hydrocarbons to olefins and then react the olefins to produce the hetero organic compounds. While this route to many commercial chemicals has been widely adapted in the industry, it is clear that the direct conversion of saturated hydrocarbons to hetero organic chemicals would be preferable since a major step in the process would be eliminated, thereby resulting in substantial economic benefits.
The fundamental problem in converting saturated hydrocarbons directly to hetero organic compounds is the high stability of the Cxe2x80x94C and Cxe2x80x94H bonds. In view of the high stability of these bonds, attempts to directly convert saturated hydrocarbons to hetero organic molecules have met with few successes. For example U.S. Pat. No. 2,874,186 discloses a process for reacting carbon monoxide with normal paraffins, isoparaffins and naphthenes to produce ketones, acids and esters. The process involves placing the isoparaffin in a reactor with hydrogen fluoride and boron trifluoride (HF/BF3) and carbon monoxide under high pressures. The products, which were obtained from this process, were ketones and carboxylic acids. U.S. Pat. No. 2,346,701 discloses preparing organic oxygen-containing compounds such as ketones and acids by reacting propane with carbon monoxide using an anhydrous aluminum halide catalyst, e.g., aluminum chloride. U.S. Pat. No. 3,356,720 discloses preparing oxygenated organic compounds by reacting saturated hydrocarbons with carbon monoxide using a Freidel-Crafts catalyst and a tertiary alkyl, phenyl alkyl or phenyl carbonyl halide. Both ketones and carboxylic acids are produced. It is also disclosed in WO 98/50336 that branched aliphatic hydrocarbons can be converted to branched aliphatic ketones by reacting the hydrocarbons with carbon monoxide at high pressures and super acidic conditions. The super acidic conditions are produced by the combination of a protic acid such as HF and a Lewis acid such as BF3. The reaction is carried out at temperatures of about 0xc2x0 C. to about 35xc2x0 C. and pressures of about 10 to 200 atmospheres. Both of these references use a homogeneous liquid system in which the catalyst is a highly corrosive compound. Additionally, means for separating the desired product from the reaction mixture is not disclosed and is anticipated to be very difficult.
At the EuroCat-IV meeting in Rimini, Italy, Sep. 5-10, 1999, M. V. Luzgin and A. G. Stepanov reported that isobutane can be carbonylated with carbon monoxide on sulfated zirconia at 70-150xc2x0 C. They adsorbed CO and isobutane onto sulfated zirconia and obtained the 13C NMR spectrum of the catalyst-product complex, which showed the presence of methylisopropyl ketone or pivalic acid. Finally, U.S. Pat. No. 5,679,867 discloses that arylene compounds such as toluene can be carbonylated with carbon monoxide over a solid acid catalyst such as promoted sulfated zirconia to give tolualdehyde.
In contrast to the above references, applicants have developed a process by which saturated hydrocarbons are reacted with carbon monoxide over a solid strong acid catalyst such as sulfated zirconia to give a high yield of an oxygenated saturated hydrocarbon. By oxygenated is meant an oxygen containing saturated hydrocarbon. A specific example is the carbonylation of isobutane to methylisopropyl ketone over sulfated zirconia. Hydrogenation of the oxygenate, e.g., ketone can simultaneously occur by adding a hydrogenation component to the solid catalyst and a reducing agent such as hydrogen. Alternatively, hydrogenation can be carried out in a separate step and reactor.
This invention relates to the carbonylation of saturated hydrocarbons to provide an oxygenated saturated hydrocarbon. Accordingly, one embodiment of the invention is a process for preparing an oxygenated saturated hydrocarbon comprising contacting a saturated hydrocarbon with carbon monoxide and a solid strong acid catalyst at reaction conditions to provide an oxygenated saturated hydrocarbon product.
Another embodiment of the invention is the reductive carbonylation of saturated hydrocarbons comprising contacting the saturated hydrocarbon with carbon monoxide and a hydrogen source in the presence of a strong acid catalyst containing a hydrogenation catalyst component at reductive carbonylation conditions to provide a reduced oxygenated saturated hydrocarbon product.
These and other objects and embodiments will become clearer after a detailed description of the invention.
Generally, the present invention relates to the direct carbonylation of saturated hydrocarbons to form the corresponding oxygenated saturated hydrocarbons. As stated, by oxygenate is meant an oxygen containing saturated hydrocarbon, with saturated referring to the hydrocarbon portion of the molecule. Non-limiting examples of these oxygenates are ketones aldehydes and acids. Without wishing to be bound by any particular theory, the reaction pathway by which direct carbonylation to ketones takes place involves the formation of a carbocation species, i.e., a carbenium or carbonium ion which is then reacted, i.e., intercepted, by carbon monoxide molecules forming a relatively stable oxycarbocation. The oxycarbocation undergoes further molecular rearrangement involving an intramolecular hydrogen transfer, i.e., hydride shift, to produce an aldehyde, and an intramolecular methyl shift to convert the aldehyde to the more stable ketone.
Accordingly, those saturated hydrocarbon compounds, which can be used in the present invention, are any of those that can form a carbocation at reaction conditions. The hydrocarbons, which meet these criteria, are any of those which contain at least one of a primary , secondary or tertiary carbon as described in standard organic chemistry texts. Preferred hydrocarbons are those which contain one or more tertiary carbon. For the purpose of this invention, the hydrocarbons which meet these criteria are the saturated hydrocarbons which include alkanes and cyclic alkanes. Although the number of carbon atoms which the saturated hydrocarbons can have is not a critical aspect of this invention, for practical purposes those having 1 to 30 carbon atoms are usually used and thus are preferred.
Included in the general category of alkanes are straight chain alkanes, single and multiple branched alkanes. Cyclic alkanes include cyclic alkanes having one or more alkyl groups attached to the ring. Especially preferred alkanes are the branched alkanes (branched such that they contain one or more tertiary carbon) having from 4 to about 30 carbon atoms. Specific examples of branched alkanes include, but are not limited to, isobutane, isooctane, methylcyclopentane, methylcyclohexane, 2,3-dimethylbutane and 2-methylundecane. Further, mixtures of any of the C4-C30 alkanes can be used in the process and indeed mixtures can lead to very useful products. Examples of these mixtures include, but are not limited to, mixtures of butane and isobutane; mixtures of C6 isomers including 2,2-dimethyl butane, 2,3 dimethyl butane, 2-methyl pentane, 3-methyl pentane and n-hexanes; detergent range isoparaffins which usually include C10 to C16 isoparaffins; etc. It should be pointed out that the initial hydrocarbon feed, in the presence of the strong acid catalyst at reaction conditions, can undergo isomerization from unbranched to branched (tertiary carbon) hydrocarbons. Thus, the preferred hydrocarbons can be generated in situ.
A solid strong acid catalyst is required to react the hydrocarbon with carbon monoxide. Liquid acids whose strength is greater than sulfuric acid have been termed xe2x80x9csuperacidsxe2x80x9d. A number of liquid super acids are known in the literature including substituted protic acids, e.g., trifluoromethyl substituted H2SO4, triflic acid and protic acids activated by Lewis acids (HF plus BF3). While determination of the acid strength of liquid super acids is relatively straightforward, the exact acid strength of a solid strong acid is difficult to directly measure with any precision because of the less defined nature of the surface state of solids relative to the fully solvated molecules found in liquids. Accordingly, there is no generally applicable correlation between liquid super acids and solid strong acids such that if a liquid super acid is found to catalyze a reaction, there is no corresponding solid strong acid which one can automatically choose to carry out the same reaction. Therefore, as will be used in this specification, xe2x80x9csolid strong acidsxe2x80x9d are those that have an acid strength greater than sulfonic acid resins such as Amberlyst(copyright)-15. Additionally, since there is disagreement in the literature whether some of these solid acids are xe2x80x9csuperacidsxe2x80x9d only the term solid strong acid as defined above will be used herein.
Another way to define a solid strong acid is a solid comprising of interacting protic and Lewis acid sites. Thus, solid strong acids can be a combination of a Bronsted (protonic) acid and a Lewis acid component. In other cases, the Bronsted and Lewis acid components are not readily identified or present as distinct species, yet they meet the above criteria.
Examples of the solid acids which fall within the bounds of this invention include but are not limited to sulfated metal oxides (especially sulfated zirconia), fluorocarbon sulfonates (xe2x80x94(CF2)nxe2x80x94SO3H) in combination with supports (e.g. metal oxides and carbon), heteropolyacids, halides of Ta, Sb, Ga and B in combination with halogenated metal oxides, sulfated zeolites, halides of Ta, Sb, Ga and B in combination with fluorosulfonic acid resins, Nafion(copyright) and substituted Nafion(copyright). Nafion(copyright) is a perfluorinated copolymer of tetrafluoro-ethylene and perfluoro-3,6 dioxa-4methyl-7-octenesulfonic acid. Nafion(copyright) can be substituted by treating with a Lewis acid including but not limited to AlCl3, TaF5, SbF5. It should be pointed out that metal oxides as used herein include both single component oxides or multi-component oxides, i.e., mixed metal oxides. Single component metal oxides include but are not limited to aluminas, silicas, zirconia, titania and mixtures thereof. The mixed metal oxides can be either physical mixtures or preferably structurally connected. Examples of mixed metal oxides include but are not limited to Zrxe2x80x94Ti, Wxe2x80x94Zr, Tixe2x80x94Cu, Tixe2x80x94Zn, Tixe2x80x94Si, Alxe2x80x94Zr, Fexe2x80x94Zr and Tixe2x80x94Mn oxides. Specific examples of the solid strong acids include, but are not limited to, sulfated zirconia, sulfated titania, sulfated tungsten oxide, BF3 on fluorinated alumina, aluminum chloride on chlorinated alumina, TaF5 in combination with Nafion(copyright), H3PW10O40, Cs2.5H0.5PW12O40, H4SiW12O40, etc.
The synthesis of the above named solid strong acids can be carried out using conventional techniques known in the art and will be repeated here only for completeness. For example, there are numerous methods of preparing sulfated zirconia, which are reviewed in xe2x80x9cCatalysis Reviewxe2x80x9dxe2x80x94Sci. Eng. 38 (3), 329-412, 1996. Generally, the method involves hydrolyzing a zirconium salt, such as ZrOCl2 or ZrO (NO3)2 with aqueous ammonia to produce zirconium hydroxide. Next the zirconium hydroxide is treated with dilute sulfuric acid or (NH4)2 SO4 solution followed by drying. The resultant sulfated zirconium hydroxide is calcined in air at 550xc2x0 C. to about 650xc2x0 C. to generate strong acidity. Aluminum chloride on alumina or chlorinated alumina is also a well-known solid strong acid, which can be synthesized by vapor deposition of sublimed aluminum chloride on chlorinated alumina at high temperatures. Chlorinated alumina is in turn prepared by treatment of gamma alumina with hydrochloric acid.
Promoters can also be incorporated with the solid strong acid in order to increase catalyst activity for specific reactions. Thus, sulfated zirconia can be promoted by elements such as V, Cr, Co, Ni, Fe, Cu, Mo, Mn, W, the lanthanide elements and mixtures thereof. Preferred promoters are Fe, Mn, Ce, Cr, Ni and W. These promoters can be incorporated or combined with the solid acid catalyst by means well known in the art such as impregnation, spray drying, coprecipitation etc. Specific examples are provided in the examples. The final promoter may be in the form of the metal oxide, reduced metal or become chemically part of the strong acid structure.
The solid strong acid catalyst can also have a hydrogenation catalyst component in order to reduce the oxygenates, e.g., ketones to reduced oxygenates, for example alcohols. In this case the process is called reductive carbonylation. Hydrogenation catalyst components include but are not limited to Group VIII metals of the Periodic Table, molybdenum, tungsten and mixtures thereof. Preferred hydrogenation components are the platinum group metals. The platinum group metals are platinum, palladium, rhodium, iridium, ruthenium and osmium. Preferred platinum group metals are platinum and palladium. The hydrogenation catalyst component is present in an amount from about 1 to about 10 wt. % as the metal. Accordingly, these hydrogenation components are incorporated or combined with the solid acid catalyst by the same means as the promoters described above. The hydrogenation component and promoter can be added in any order including simultaneously although not necessarily with equivalent results. The hydrogenation is carried out with a hydrogen containing gas.
The carbonylation reaction is conducted by contacting the desired saturated hydrocarbon feed and carbon monoxide with the solid strong acid catalyst. The three components can be mixed in any order although not necessarily with equivalent results. The process can be carried out in either a batch process or a continuous flow process. In a batch process one way of carrying out the process involves placing the catalyst in an autoclave followed by the addition of the desired hydrocarbon and finally, pressuring with carbon monoxide. Of course the reverse addition can also be done, i.e., carbon monoxide first and then hydrocarbon. The pressure of carbon monoxide can vary considerably but usually, is between 345 kPa to about 27,580 kPa (50 to 4,000 psig). The autoclave is then heated to a temperature of about 20xc2x0 C. to about 200xc2x0 C. and preferably from about 50xc2x0 C. to about 150xc2x0 C. for a time sufficient to form the desired oxygenated hydrocarbon. The time varies from about 1 min. to about 20 hrs. After the desired time has elapsed, the autoclave is vented. Depending on the choice of hydrocarbon, conditions and catalyst, the product may be in solution or chemically attached to the catalyst.
As used in the present application, attached includes either physical adsorption or chemical e.g., ionic complex. If the product is attached to the catalyst, then the catalyst is treated in order to remove the product attached to the catalyst. The catalyst can be heated such that the product is thermally desorbed. Alternatively, a suitable solvent or chemical displacing agent can be used. Examples of these include but are not limited to water, steam, and organic solvents such as but not limited to methanol, ethanol, acetonitrile, hexamethylbenzene, etc. Polar solvents are preferred.
As stated, the product obtained from the carbonylation of saturated hydrocarbon with carbon monoxide is an oxygenated saturated hydrocarbon. The major product will be a ketone, with other products being carboxylic acids and aldehydes. If the alkane or cyclic alkane has more than one tertiary carbon, e.g., di, tri, or poly tertiary carbons, then di, tri or poly oxygenated saturated hydrocarbons can be obtained. Of course, as stated above the hydrocarbon feed can be a mixture of species and thus a mixture of mono, di, or poly oxygenated products can be obtained.
In a continuous mode, the catalyst may be employed as a fixed bed over which are flowed a mixture of carbon monoxide and the chosen saturated hydrocarbon(s). In this case, the reaction mixture is flowed over the catalyst at a space velocity of about 0.01 to about 10 hrxe2x88x921, while maintaining a pressure of about 345 kPa to about 27,580 kPa (50 to about 4,000 psig) at a temperature of about 20xc2x0 C. to about 200xc2x0 C.
If the solid strong acid also contains a hydrogenation component, then instead of adding only carbon monoxide, a mixture of carbon monoxide and hydrogen is used. The ratio of CO/H2 can vary considerably but usually is from about 1 to about 90 and preferably from about 0.5 to about 2. Further, the ratio of H2 to oxygenated hydrocarbon varies from about 1 to about 10. The carbon monoxide and hydrogen can be introduced separately, premixed and introduced as one gas or snygas can be used. It should be pointed out that for C1 to C3 hydrocarbons, i.e., methane, ethane and propane, although carbonylation can be carried out (see example 11) reductive carbonylation is preferred in order to drive the carbonylation reaction. In this case one obtains reduced oxygenated saturated hydrocarbons which are mostly alcohols.
Alternatively, hydrogenation of the oxygenated hydrocarbon can be carried out in a separate step. In this case, the oxygenated hydrocarbon is reacted with a hydrogen containing gas in the presence of a hydrogenation catalyst to give the corresponding reduced oxygenated hydrocarbon. Again, the process can be carried out in a batch or continuous mode with continuous mode being preferred. Hydrogenation conditions include a temperature of about 20xc2x0 C. to about 200xc2x0 C., a pressure of about 345 kPa to about 27,580 kPa (50 to about 4,000 psig) and a liquid hourly space velocity of about 0.5 to about 10 hrxe2x88x921. In a batch mode the contact time varies from about 1 minute to about 5 hrs.
The hydrogenation catalyst comprises a hydrogenation component dispersed on a suitable support. The hydrogenation components are the same as enumerated above. The support can be any support, which is inert to the reactants and products and has a sufficient surface area in order to disperse the hydrogenation component thereon. The surface area should be at least 5 m2/g. Specific examples include, but are not limited to, metal oxides, organic polymers, halogenated metal oxides, carbon and fluorinated carbon. These hydrogenation catalysts are prepared by conventional techniques in which one or more hydrogenation metal compounds are dissolved in a suitable solvent and then contacted with the support. Contacting can be done by impregnation, spray drying, etc. As stated above, the final form of the hydrogenation component can be a metal, metal oxide or a metal compound. Finally, the concentration of the hydrogenation component can vary from about 1 to about 10 wt. % of the catalyst as the metal.
The oxygenated (or reduced oxygenated) hydrocarbons of this invention have various uses as solvents, gasoline additives, surfactants, monomers for polymers, etc.